Jet engines, and particularly the compressors of aircraft jet engines and helicopter turbo-shaft engines, are subject to contamination from the ingestion of general airborne pollution, as well as unburned hydrocarbons (soot), lubricating oil vapors etc., emanating from other aircraft engines when maneuvering around airports and on take-off and landing. Such contamination can lower engine efficiency, lead to undesirable increases in exhaust gas temperature and in extreme cases can result in engine failure.
Accordingly, to maintain engine fuel efficiency and power output, as well as the avoidance of potential engine failure, the cleaning of the gas path of jet engines is recommended and, in many cases, is now a requirement mandated by engine OEMs in order to assure and maintain performance guarantees. Such cleaning may be as part of non-preventative maintenance and/or performance recovery procedures, as well as being performed as a routine preventive maintenance procedure to help extend the useful life of hot-end components by helping to keep exhaust gas temperatures within required or desired limits. Cleaning of a jet engine helps to maintain its overall efficiency, as even moderately dirty engine can easily result in about a 0.5 to 1.5% increase in fuel consumption. Regular or programmed engine washing, when done properly, is thus a relatively inexpensive way of conserving resources and saving significant amounts of money. And given the prodigious amounts of jet fuel used on a daily basis and today's high fuel costs, keeping jet engines clean can directly affect an airline's bottom line. Similarly, periodic cleaning of the compressors of helicopter turbine engines—which can become even more fouled than jet engines because of their lower and more polluted operating heights—is a necessity to maintain fuel efficiency and engine reliability and avoid potential catastrophic failure.
While the cleaning of a jet engine can be accomplished as part of the disassembly of the engine, engine cleaning, particularly as a preventive maintenance act and/or to combat excess fuel burn, is normally performed with the engine in-situ on the aircraft. This is commonly referred to as on-the-wing-cleaning.
Effective cleaning requires that the stator and rotor blades of the engine compressor be uniformly cleaned and flushed. On-the-wing hand-cleaning is almost totally ineffective because only the first few stages of the compressor are accessible by hand; most of the compressor remains uncleaned. There is also no possibility whatsoever of hand cleaning any part of the combustion system or turbine, so an effective cleaning system or method most be designed to reach all the rotor and stator elements throughout the entire engine assembly.
A commonly utilized method for the cleaning of a jet engine comprises the spraying of a cleaning liquid into the engine compressor inlet as it is operated in the dry cranking mode of the engine's starting system using compressed air from the aircraft's own auxiliary power unit (APU) or an external source of ground power as its motive power. This is commonly known as a “motoring wash” in which the engine is turned or motored (with fuel isolated) up to a selected speed (typically between 10 to 20% of its N2 shaft speed). By motoring, or cranking the engine in this manner sufficient air flow is generated through the engine to effectively draw in the cleaning and rinse solutions, which break down and wash off the accumulated foulant from the compressor section. Some of the removed foulant will be carried in the air flow completely through the engine and be expelled with the exhaust flow, thus having a secondary cleaning effect on the turbine section, while some may drain away by gravity with the wash fluid and rinse water to the lower half of the engine where it can be collected and drained to a tank or receptacle for safe disposal or separation after the engine wash procedure is completed.
Often the cleaning liquid is warm or hot water (typically in the range of 70 to 200° F.) either alone or with the addition of detergent-type additives. In earlier times—before the development of cooled turbine blades by pre-heated bleed air from the compressor—mild abrasives such as rice husks, crushed pecan shells or carbon based powders were injected into the compressor to scour the airfoils and removed surface deposits. However, with the introduction of turbine cooling by compressor bleed air—now utilized in the vast majority of gas turbines and jet engines—the use of such solid abrasives came to an end in these types of gas turbines because of the danger of blade cooling channels and ports being plugged up by the cleaning abrasive itself and the subsequent and rapid high temperature failure of turbine blades.
For jet engine or turbojet cleaning the cleaning solution and rinse water spray nozzles are often affixed to simple hand-held wands that are manipulated across the area of the engine inlet by maintenance personnel, although uniformity of cleaning is very difficult to achieve with this procedure. In addition, this cleaning method requires the operator to stand directly in front of the engine inlet while it is being motored, thus potentially creating a very serious hazard to the operator and the engine.
U.S. Pat. No. 8,109,807 discloses a cleaning system that consists of a disc carrying a number of spray nozzles which is held against the engine's central “spinner” by a bolting system which attaches to and through the fan blades of the engine. The cleaning solution and rinse water is delivered to the nozzles through a rotational coupling which attaches to the center of the nozzle disc. As the engine is spooled up by its starting system the disc and its nozzles rotate with the spinner and the wash solution and rinse water is injected though the fan blades and into the compressor of the engine core.
In another process, as set forth in U.S. Pat. No. 4,170,489, cleaning solution is dispensed through the engine's fuel nozzles themselves. This is only suitable for potential cleaning of the fuel nozzles, combustors and turbine and not the compressor, which is the source of most engine fouling and performance loss. Dispensed detergent mixture is introduced and allowed to remain on the fuel nozzles for a soak period, followed by a pulsating detergent spray followed in turn by a pressurized alt purge to clear the fuel nozzles and dry the internal surfaces of the combustion system and turbine.
In the system disclosed in U.S. Pat. No. 8,444,773, a J-hook on a Song lance is introduced into the engine from the rear and affixed-to the lip of the core engine compressor inlet. Cleaning solution and rinse water is injected into the compressor. The entire engine is also wrapped m a waterproof cover to collect the drainage.
Conventional jet engine wash systems and techniques, such as those described above, typically require either continued monitoring and positioning of the spray equipment by personnel or the affixation of the spray devices to the engine. Such procedures can be time intensive, require careful alignment and positioning, and can result in very serious damage to the engine if not carefully positioned and retained properly. Accordingly, there is a need for a jet engine cleaning apparatus and methodology which avoids the shortcomings of conventional systems, which does not require contact with critical engine parts or insertion into the engine interior and which allows the efficient and controlled use of cleaning solutions in a repeatable process and procedure to give consistent and predictable cleaning results.